I am knitting a D.Bliss pattern pg 87 baby cardigan(Cotton Knits for All Seasons). The back is almost complete with a total of 72 stitches . However, patt reads knit next 21 sts,turn work this set of sts only. Cont until 10 3/4 in then bind off. Take next 30 stitches join yarn cont in patt until 10 3/4 ins. Now I have three separate pieces when I believe the back should be one piece (or at least that's the way it looks in the book). So confused...any suggestions?Thank you

No, it's not just the back, it sounds like 2 fronts and the back so there should be 3 sections. The whole body was in one piece, but at the underarms you work the back and fronts separately, then join at the shoulders.